Motion analysis system and azimuth tuning method

ABSTRACT

A motion analysis system includes an analysis control device that analyzes a motion of a measurement target using measurement data from a plurality of measurement units including an angular velocity sensor, and the analysis control device receives measurement data based on a first rotational motion around a first rotation axis of the measurement target from the plurality of measurement units when an axis intersecting a perpendicular line with respect to a first plane in a space including the measurement target is set as the first rotation axis, and tunes azimuths on the first plane in the plurality of measurement units using the measurement data based on the first rotational motion.

TECHNICAL FIELD

The present invention relates to a motion analysis system and an azimuth tuning method.

BACKGROUND ART

A system for analyzing a motion is required for various fields. For example, by analyzing a swing path of a golf club or a tennis racket, a movement form of pitching or batting of a baseball game, or the like and clearly finding out improvements from the analysis result, it is possible to cause performance enhancement.

For example, the invention described in PTL 1 analyzes a golf swing by the use of detection means attached to a shaft of a golf club and issues a sound corresponding to a rotational velocity of the golf club to a user. For example, when a rapid sound variation is included, it means that a backswing is not stabilized and thus the user can take a countermeasure such as correcting a form.

CITATION LIST Patent Literature

PTL 1 : JP-A-7-178210

SUMMARY OF INVENTION Technical Problem

Here, in the invention described in PTL 1, an acceleration sensor for acquiring a function of a velocity, a pressure-sensitive sensor, a pressure sensor, and the like as well as a velocity sensor may be used as the detection means. PTL 1 also mentions that such sensors are attached, for example, to a tip, a center of a shaft, and a grip portion of a golf club and a user's hand and arm to analyze a golf swing.

By detecting a velocity by the use of plural detection means, for example, it is possible to analyze a user's swing form as well as a velocity variation of the tip of the golf club. However, when axis directions of plural sensors attached as the detection means cannot be tuned to each other, it is not possible to accurately understand a direction of the velocity variation at the positions to which the sensors are attached and there is a possibility that the analysis will be inaccurate.

Here, PTL 1 mentions that the detection means is preferably detachably attached using an adhesive tape or a hook-and-loop fastener. Then, since the axis directions of the respective sensors vary every time of attachment of the plural sensors, an operation of tuning the axis directions is necessary. However, PTL 1 does not describe any method or operation of tuning the axis directions of the plural sensors.

Here, a technique of disposing a geomagnetic sensor, which can detect a geo-magnetic direction and calculate an azimuth, in each of all the detection means can be considered. However, it is not possible to correctly tune the axis directions in locations at which a geomagnetic field greatly fluctuates. Otherwise, a technique of performing an initial operation of arranging plural detection means to be directed to the same direction can also be considered. However, this initial operation is a troublesome operation for a user and is not realistic.

An advantage of some aspects of the invention is to provide a motion analysis system which can tune axis directions of plural sensors used to detect a motion after attachment thereof and can accurately analyze a motion. Here, the analysis of a motion means to analyze, for example, a position, a velocity, and an acceleration of a specific part based on a motion of a measurement target.

Solution to Problem

The invention can be implemented as the following forms or application examples.

APPLICATION EXAMPLE 1

This application example is directed to a motion analysis system including an analysis control device that analyzes a motion of a measurement target using measurement data from a plurality of measurement units including an angular velocity sensor, wherein the analysis control device receives measurement data based on a first rotational motion around a first rotation axis of the measurement target from the plurality of measurement units, and tunes azimuths on a first plane in the plurality of measurement units using the measurement data based on the first rotational motion.

APPLICATION EXAMPLE 2

The motion analysis system according to the application example described above may be configured such that the first rotation axis is an axis intersecting a perpendicular line with respect to the first plane.

APPLICATION EXAMPLE 3

The motion analysis system according to the application example described above may be configured such that a first transform expression including information of the first rotation axis is acquired for each measurement unit, and the azimuths on the first plane in the plurality of measurement units are tuned using the first transform expressions.

APPLICATION EXAMPLE 4

The motion analysis system according to the application example described above may be configured such that the first plane is a horizontal plane.

The motion analysis system according to this application example includes the analysis control device that receives measurement data from plural measurement units. Each measurement unit includes at least an angular velocity sensor and can detect an angular velocity based on, for example, a rotational motion of the measurement target. Therefore, the measurement data received by the analysis control device is physical quantity data including at least the angular velocity. The measurement target may be a person or an object.

Here, the plural measurement units are attached to different parts of the measurement target and the like and directions of the measurement units are not tuned. For example, when each measurement unit includes a three-axis angular velocity sensor of an x axis, a y axis, and a z axis, the directions of the respective x axis, the y axis, and the z axis of the angular velocity sensors of the measurement units are not aligned with one another. Therefore, a motion detected as an angular velocity around the x axis in the measurement data of a certain measurement unit may be detected as an angular velocity around the z axis in the measurement data of another measurement unit. When a process of tuning the axes of the measurement units to each other is not carried out, the analysis control device cannot accurately analyze a motion of a measurement target on the basis of the measurement data.

According to this application example, the analysis control device receives the measurement data based on the first rotational motion of the measurement target having the first rotation axis from the plural measurement units. Then, the analysis control device may acquire the first transform expression including the information of the first rotation axis on the basis of the measurement data for each measurement unit. Here, the first rotational motion does not need to describe, for example, a circle, and has only to describe an arc sufficient to specify the first rotation axis.

The first transform expression may be, for example, a quaternion which enables a rotation of an arbitrary axis. For example, a rotation axis vector which is the information of the first rotation axis can be easily acquired from the quaternion.

Here, the first rotation axis is not parallel to the perpendicular line put down onto the first plane which is a plane in a space. Accordingly, when the first rotation axis is projected onto the first plane, a straight line (hereinafter, referred to as “projected line”) of which the size is not zero is obtained. For each measurement unit, by setting an angle formed by the “projected line” obtained from the first transform expression and the direction about the first plane as a reference as an azimuth angle, it is possible to tune the azimuths on the first plane in the plural measurement units.

Accordingly, the motion analysis system according to this application example can tune the axis directions of the plural measurement units including plural sensors used to detect a motion after the measurement units are attached to a measurement target. The motion analysis system according to this application example can accurately analyze a motion of the measurement target.

The direction on the first plane as a reference may be determined on the basis of the rotation axis of one measurement unit or may be determined using one axis (for example, the x axis) of an absolute coordinate system (global coordinate system). From the viewpoint of reduction of a calculation load, it is preferable that the direction about the first plane be determined on the basis of the rotation axis of one measurement unit.

In general, an azimuth and an azimuth angle are often used for a horizontal plane, but the terms such as an azimuth and an azimuth angle are used for a plane other than the horizontal plane in this specification. That is, even when a certain plane is not a horizontal plane, a reference direction thereof is defined and the azimuth and the azimuth angle are defined on the basis of the relationship with the reference direction on the plane.

The first plane is a virtual plane in a space including a measurement target (the same is true of a second plane to be described later). The movement of the measurement target includes a stop state as well as a motion state of the measurement target.

APPLICATION EXAMPLE 5

The motion analysis system according to the application example described above may be configured such that each of the plurality of measurement units includes an acceleration sensor, and the analysis control device tunes the azimuths in an elevation angle direction about the first plane in the plurality of measurement units using information of a gravitational acceleration included in the measurement data of the acceleration sensors when the measurement target stops.

APPLICATION EXAMPLE 6

The motion analysis system according to the application example described above may be configured such that the analysis control device receives measurement data based on a second rotational motion around a second rotation axis of the measurement target from the plurality of measurement units when an axis intersecting a perpendicular line with respect to a second plane perpendicular to the first plane is set as the second rotation axis, and tunes azimuths on the second plane in the plurality of measurement units using the measurement data based on the second rotational motion.

The analysis control device of the motion analysis system according to this application example may detect the direction of the perpendicular line put down onto the first plane which is a horizontal plane on the basis of the gravitational acceleration. Here, each measurement unit includes an acceleration sensor as well as the angular velocity sensor. Accordingly, the analysis control device can calculate a direction (hereinafter, also referred to as a vertical direction) perpendicular to the horizontal plane for each measurement unit on the basis of the gravitational acceleration included in the measurement data based on the stop state of the measurement target. That is, since the angle formed by the direction of the gravitational acceleration and one axis (for example, a z axis) of each measurement unit can be found, it is possible to accurately find the vertical direction.

The analysis control device can tune the azimuth of the horizontal plane as the first plane in the plural measurement units. Since the vertical direction can be accurately found, the azimuths in the elevation angle direction about the first plane can be tuned in the plural measurement units. That is, it is possible to implement a motion analysis system which can three-dimensionally tune the axis directions of the plural sensors used to detect a motion after attachment and can accurately analyze a motion.

The analysis control device of the motion analysis system according to this application example may tune the azimuths on a second plane perpendicularly intersecting the first plane in the plural measurement units on the basis of a second rotational motion instead of the gravitational acceleration. Here, the second rotational motion is a motion around the second rotation axis which is not parallel to the vertical line put down onto the second plane perpendicularly intersecting the first plane. The azimuths on the second plane can be tuned using information of the second rotation axis in the same technique as tuning the azimuths on the first plane in the plural measurement units using the information of the first rotation axis.

Since the analysis control device of the motion analysis system according to this application example can tune the azimuths on the first plane and the azimuths (which are the elevation angle about the first plane) on the second plane in the plural measurement units, it is possible to implement a motion analysis system which can three-dimensionally tune the axis directions of the plural sensors used to detect a motion after attachment and can accurately analyze a motion. The gravitational acceleration measured by the acceleration sensor does not need to be used to tune the axis directions and the measurement target does not need to be stopped.

APPLICATION EXAMPLE 7

The motion analysis system according to the application example described above may be configured such that the measurement units are attached to at least one of exercise equipment and a test subject.

APPLICATION EXAMPLE 8

The motion analysis system according to the application example described above may be configured such that the analysis control device uses at least a part of a swing motion as the first rotational motion.

The analysis control device of the motion analysis system according to this application example receives the measurement data from the measurement units attached to at least one of the exercise equipment and the measurement target and analyzes a swing motion using the exercise equipment of the measurement target. Here, the measurement target is a user of the exercise equipment. Since the analysis control device acquires the measurement data of the exercise equipment as well as the measurement target, it is possible to more accurately analyze a swing motion including a force delivery method or the like.

The analysis control device may use at least a part of the swing motion as the first rotational motion. Here, the user can tune the azimuths of the plural measurement units without performing an unnecessary operation other than the swing motion.

Here, the entire swing motion may be used as the first rotational motion but only a partial swing motion close to a rotational motion may be used as the first rotational motion. For example, when the swing motion is a golf swing, a partial motion just before impact in which the head speed is high and a curve is drawn may be used as the first rotational motion.

On the other hand, the analysis control device may use a motion other than the swing motion as the first rotational motion. Here, it is possible to accurately tune the azimuths of the plural measurement units using the first rotational motion other than the swing motion.

For example, when the swing motion is a golf swing, a motion in which a golf club moves up and down, which is different in movement from the golf swing, may be used as the first rotational motion. When the second rotational motion is performed, at least a part of the swing motion may be used as the second rotational motion or a motion different from the swing motion may be used as the second rotational motion.

APPLICATION EXAMPLE 9

The motion analysis system according to the application example described above may be configured such that the motion analysis system further includes the plurality of measurement units.

APPLICATION EXAMPLE 10

This application example is directed to an azimuth tuning method including: receiving measurement data based on a first rotational motion around a first rotation axis of a measurement target from a plurality of measurement units including an angular velocity sensor; and tuning azimuths on a first plane in the plurality of measurement units using the measurement data based on the first rotational motion.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration example of a motion analysis system according to a first embodiment.

FIG. 2 is a diagram illustrating an example where a golf swing is measured using the motion analysis system according to the first embodiment.

FIG. 3 is a diagram illustrating an example of a path of a golf swing.

FIG. 4 is a block diagram illustrating a measurement unit.

FIG. 5 is a block diagram illustrating an analysis control device.

FIG. 6 is a diagram illustrating a state where azimuths are not tuned when measurement units are attached.

FIG. 7A is a diagram illustrating a rotational motion used for azimuth tuning.

FIG. 7B is a diagram illustrating a rotational motion used for azimuth tuning.

FIG. 8 is a flowchart illustrating a process flow in the measurement unit of the motion analysis system according to the first embodiment.

FIG. 9 is a flowchart illustrating a process flow in an analysis control device of the motion analysis system according to the first embodiment.

FIG. 10 is a flowchart illustrating a process flow of a measurement unit in a motion analysis system according to a second embodiment.

FIG. 11 is a flowchart illustrating a process flow in an analysis control device of the motion analysis system according to the second embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments of the invention will be described in detail with reference to the accompanying drawings. The embodiments to be described below do not unduly limit details of the invention described in the appended claims. All elements to be described below are not limited as essential elements of the invention.

1. First Embodiment

Configuration of Motion Analysis System

FIG. 1 is a diagram illustrating a configuration example of a motion analysis system 1 according to this embodiment. The motion analysis system 1 includes plural measurement units 10-1 and 10-2 and an analysis control device 20.

The motion analysis system 1 includes two measurement units 10-1 and 10-2 but may include three or more measurement units. In this embodiment, the analysis control device 20 and the measurement units 10-1 and 10-2 are connected to each other in a wireless manner, and a degree of freedom in arrangement of the measurement units 10-1 and 10-2 in the motion analysis system 1 is high. That is, the measurement units 10-1 and 10-2 can be freely attached to, for example, exercise equipment or a user, for example, using adhesive tapes or hook-and-loop fasteners.

The analysis control device 20 and the measurement units 10-1 and 10-2 may communicate with each other in a multicast or broadcast manner or may communicate with each other in a unicast manner so as to suppress band consumption. Measurement data is wirelessly transmitted from the measurement units 10-1 and 10-2 to the analysis control device 20, and a control signal such as a measurement start command is wirelessly transmitted from the analysis control device 20 to the measurement units 10-1 and 10-2.

The measurement units 10-1 and 10-2 are attached to, for example, a measurement target or exercise equipment (for example, a golf club or a tennis racket) which is a target of motion analysis. The measurement target may be an object, but is a user of the motion analysis system 1 (hereinafter, simply referred to as a user) in this embodiment. The motion analysis system 1 can be applied to analysis of various motions, but is used to analyze a golf swing in this embodiment (see FIG. 2).

The measurement units 10-1 and 10-2 include inertial sensors 111-1 and 111-2, respectively. The inertial sensors 111-1 and 111-2 create measurement data including accelerations and angular velocities (corresponding to physical quantities of the invention) generated by causing a user to make a golf swing.

The analysis control device 20 includes a motion analysis unit 201 that performs motion analysis of a measurement target and a main control unit 203 that controls the entire motion analysis system 1 as well as the analysis control device 20. In this embodiment, the analysis control device 20 is embodied by a personal computer (PC). A CPU 200 serves as the motion analysis unit 201 and the main control unit 203 in accordance with a program.

The motion analysis unit 201 of the analysis control device 20 receives measurement data from the measurement units 10-1 and 10-2. The motion analysis unit performs the motion analysis by tuning the axes (specifically, the x axis, the y axis, and the z axis) of the measurement units 10-1 and 10-2 using the measurement data based on a stop state of a measurement target and a first rotational motion of the measurement target. Accordingly, the analysis control device 20 can accurately analyze the motion of the measurement target. The measurement units 10-1 and 10-2 are not attached in a state where the axes of the measurement units 10-1 and 10-2 are tuned. That is, the axis directions of the measurement units 10-1 and 10-2 are unconnected to each other. The rotation axis of the first rotational motion is not parallel to the direction of a gravitational acceleration (vertical direction).

The schematic configuration of the motion analysis system 1 is described above with reference to FIG. 1 and detailed block diagrams of the measurement units 10-1 and 10-2 and the analysis control device 20 will be described later. The measurement units 10-1 and 10-2 have the same configuration. “-1” and “-2” included in the reference signs are used to individually distinguish the plural measurement units 10 from each other and do not mean that the configurations thereof are different from each other. In the following description, the measurement units 10-1 and 10-2 may be described to be the measurement unit 10 without any particular mention for the purpose of avoidance of repeated description. The inertial sensors 111-1 and 111-2 may be described to be the inertial sensor 111.

In the motion analysis system 1 according to this embodiment, the analysis control device 20 is embodied by a PC, but may be embodied by dedicated hardware. In this case, at least one of the motion analysis unit 201 and the main control unit 203 may be embodied by dedicated hardware instead of the CPU 200.

FIG. 2 is a diagram illustrating an example where a golf swing is measured using the motion analysis system 1. A user swings a golf club 30. In this case, the measurement unit 10-1 is attached to the golf club 30 and the measurement unit 10-2 is attached to the user's wrist. The measurement units 10-1 and 10-2 measure the acceleration and the angular velocity in the golf swing of the golf club 30 and the user's wrist, respectively.

The measurement unit 10 includes a three-axis (x axis, y axis, and z axis) acceleration sensor and a three-axis (x axis, y axis, and z axis) angular velocity sensor. The acceleration sensor measures accelerations in the x axis direction, the y axis direction, and the z axis direction and outputs the measured acceleration data. The angular velocity sensor measures the angular velocities around the x axis, the y axis, and the z axis and outputs the measured angular velocity data.

FIG. 3 illustrates a swing path A of a club head of the golf club 30. The swing path A includes a swing start position P1, a top position P2, an impact position P3, and a follow-through top position P4. The motion analysis system 1 analyzes how the user moves (exercises) the wrist in the swing path A and provides information helpful for improvement, as well as displays the swing path A.

For example, in analysis of a golf swing, a variation of an angle (cock) formed by the wrist and the golf club 30 in swing or an uncock timing at which a force maintained in the first half of a down swing is loosened and the angle of the wrist and the golf club 30 starts increasing is analyzed. When the uncock timing is too early, it can be determined that the club head is not satisfactorily accelerated toward the impact position.

In order to correctly perform such determination, the motion analysis system 1 needs to tune the axis directions of the measurement units 10-1 and 10-2 and then to cause the measurement data thereof to correspond to each other. That is, since the measurement units 10-1 and 10-2 are attached to the golf club 30 and the user's wrist using hook-and-loop fasteners, the axis directions of the measurement units 10-1 and 10-2 are not matched with each other and are different for every attachment. Therefore, when the axis directions of the measurement units 10-1 and 10-2 are not tuned to each other, it is not possible to accurately analyze a golf swing.

Therefore, in the motion analysis system 1, the axis directions of the measurement units 10-1 and 10-2 can be tuned on the basis of the direction of the gravitational acceleration and the rotation axis (first rotation axis) of the first rotational motion and it is thus possible to accurately analyze a golf swing. Detailed configurations of the measurement unit 10 and the analysis control device 20 will be first described and then a method of tuning the axis directions, that is, the three-dimensional azimuths, of plural measurement units to each other will be described.

Configuration of Measurement Unit

FIG. 4 is a block diagram illustrating the measurement unit 10. The measurement unit 10 includes a storage unit 115, a control unit 116, and a communication unit 118, in addition to the inertial sensor 111 illustrated in FIG. 1. Here, the measurement unit 10 may have a configuration in which some of the elements (units) illustrated in FIG. 4 may be omitted or modified or a configuration in which another element is added thereto.

The inertial sensor 111 includes a three-axis acceleration sensor and a three-axis angular velocity sensor as described above. Therefore, specifically, the inertial sensor 111 includes acceleration sensors 112 x, 112 y, and 112 z and angular velocity sensors 113 x, 113 y, and 113 z.

The control unit 116 samples inertial sensor data from the inertial sensor 111 with a predetermined cycle, creates measurement data, and sequentially stores the measurement data in the storage unit 115. The predetermined cycle is determined, for example, on the basis of a response frequency of the inertial sensor 111 and may be 1000 Hz or 500 Hz.

The control unit 116 receives a control signal from the analysis control device 20 via the communication unit 118. For example, when a measurement start command is given from the analysis control device 20, the control unit activates the inertial sensor 111 and starts storing the measurement data in the storage unit 115. For example, when a measurement stop command is given from the analysis control device 20, the control unit stops the storing of the measurement data in the storage unit 115 and transmits the measurement data stored in the storage unit 115 to the analysis control device 20 via the communication unit 118. The control unit 116 may be a CPU.

Configuration of Analysis Control Device

FIG. 5 is a block diagram illustrating the analysis control device 20. The analysis control device 20 includes a communication unit 210, an operation unit 220, a ROM 230, a RAM 240, a recording medium 250, and a display unit 260, in addition to the motion analysis unit 201 and the main control unit 203 illustrated in FIG. 1. The CPU 200 serves as the motion analysis unit 201 and the main control unit 203, and the motion analysis unit 201 further includes a data acquiring unit 202, a calculation unit 204, and an azimuth correcting unit 206. Here, the analysis control device 20 may have a configuration in which some of the elements (units) illustrated in FIG. 5 may be omitted or modified or a configuration in which another element is added thereto.

The communication unit 210 performs a process of receiving the measurement data from the plural measurement units 10-1 and 10-2 (see FIG. 1) and sending the received measurement data to the motion analysis unit 201. The communication unit 210 transmits the control signal (for example, the measurement start command) from the main control unit 203 to the measurement units 10-1 and 10-2.

The operation unit 220 performs a process of acquiring operation data from a user and sending the acquired operation data to the motion analysis unit 201 and the main control unit 203. For example, the operation data is data for indicating the target of motion analysis or designating details to be displayed on the display unit 260. A user may cause the motion analysis to be performed, for example, on only a motion from the top position P2 to the follow-through top position P4 through the use of the operation data and may cause the speed of the club head at the impact position P3 to be displayed (see FIG. 3).

The ROM 230 stores programs for causing the CPU 200 to serve as the motion analysis unit 201 and the main control unit 203 and to perform various calculations and control processes, or the like. The ROM 230 may store various programs or data for performing other application functions.

The RAM 240 is used as a work area of the CPU 200 and temporarily stores a program or data read from the ROM 230, data input from the operation unit 220, calculation results performed in accordance with various programs by the motion analysis unit 201, and the like.

The recording medium 250 is a computer-readable recording medium (media) storing various application programs or data. For example, an application program (program used for the motion analysis system 1) for causing a computer (PC) to serve as the analysis control device 20 may be stored therein. The recording medium 250 may serve as a recording unit that records data requiring long-term storage out of data created through the processing of the motion analysis unit 201. The recording medium 250 can be embodied, for example, by an optical disk (such as a CD or a DVD), a magneto-optical disk (MO), a magnetic disk, a hard disk, a magnetic tape, a non-volatile memory (such as an EEPROM or a flash memory), or the like.

The display unit 260 displays the processing results of the motion analysis unit 201 as characters, graphs, or other images. The display unit 260 may be embodied by, for example, a CRT, an LCD, a touch panel type display, or a head-mounted display (HMD). The functions of the operation unit 220 and the display unit 260 may be embodied by a single touch panel type display.

The CPU 200 serves as the motion analysis unit 201 and the main control unit 203 in accordance with the programs stored in the ROM 230 and the recording medium 250, and the motion analysis unit 201 further includes a data acquiring unit 202, a calculation unit 204, and an azimuth correcting unit 206. The data acquiring unit 202 receives plural pieces of measurement data via the communication unit 210.

The calculation unit 204 performs calculations necessary for analyzing a user's golf swing from the measurement data and also calculates a specific axis or direction of each of the measurement units 10-1 and 10-2. For example, the calculation unit 204 may calculate a vertical direction from the acceleration based on the stop state of the user. For example, the calculation unit 204 may calculate a first transform expression including information of the first rotation axis from the angular velocity based on the first rotational motion of the user.

The azimuth correcting unit 206 performs a calculation for tuning the azimuths of the measurement units 10-1 and 10-2. For example, the azimuth correcting unit 206 performs a calculation for tuning the vertical direction of the measurement unit 10-2 to the vertical direction of the measurement unit 10-1. For example, the azimuth correcting unit 206 performs a calculation for tuning the first rotation axis of the measurement unit 10-2 to the first rotation axis of the measurement unit 10-1 as a reference on a first plane. The azimuth correcting unit 206 may calculate an azimuth angle of the measurement unit 10-2 on the first plane and may tune the azimuths of the measurement units 10-1 and 10-2 on the basis of the calculated azimuth angle. In this embodiment, the first plane is a horizontal plane and is simply referred to as horizontal plane hereinafter.

The transform expression calculated by the calculation unit 204 is assumed to be a quaternion enabling rotation around an arbitrary axis in this embodiment. After the azimuth correcting unit 206 tunes the axes of the measurement units 10-1 and 10-2, the calculation unit 204 performs calculations necessary for analyzing the golf swing of the user.

The main control unit 203 has the same configuration as described with reference to FIG. 1 and thus detailed description thereof will not be repeated herein.

Azimuth Tuning Method of Plural Measurement Units

FIG. 6 illustrates a state where azimuths are not tuned in the motion analysis system 1 when measurement units are attached. As described above, the measurement unit 10-1 is attached to the golf club 30 and the measurement unit 10-2 is attached to the user's wrist. The measurement units 10-1 and 10-2 are attached, for example, using adhesive tapes or hook-and-loop fasteners and thus can be easily detached and attached. Accordingly, the axis directions of the measurement units 10-1 and 10-2 are unconnected to each other for every attachment and the axis directions are tuned to each other only by accident.

A method of determining one axis (hereinafter, described to be the z axis) on the basis of the gravitational acceleration is conventionally known. Since the vertical direction based on the gravitational acceleration is common in any measurement unit, it is possible to tune one axis direction by detecting the direction of the gravitational acceleration in a state where a user is stopped. Here, three axes of the measurement unit 10-1 are defined as an x1 axis, a y1 axis, and a z1 axis and three axes of the measurement unit 10-2 are defined as an x2 axis, a y2 axis, and a z2 axis. FIG. 6 illustrates a state where the z1 axis of the measurement unit 10-1 and the z2 axis of the measurement unit 10-2 are tuned on the basis of the gravitational acceleration.

However, even when the z axis direction is tuned, the x1 axis and the y1 axis of the measurement unit 10-1 and the x2 axis and the y2 axis of the measurement unit 10-2 are not tuned to each other except by accident. All of the three axes should be tuned for accurate analysis of a golf swing. For this purpose, it is necessary to know an offset, that is, an azimuth angle theta₀, from a reference direction on the horizontal plane illustrated in FIG. 6.

Therefore, in the motion analysis system 1 according to this embodiment, a user is made to execute a first rotational motion and a quaternion including information of the first rotation axis is calculated on the basis of the measurement data. A specific expression will be described later.

Here, the first rotation axis needs to be selected so as not to be parallel to the vertical direction so that a straight line with a nonzero size is obtained when the first rotation axis is put down and projected onto the horizontal plane. This is for knowing the azimuth angle theta₀ by comparing the straight lines projected onto the horizontal plane.

FIGS. 7A and 7B are diagrams illustrating the first rotational motion for tuning the azimuth on the horizontal plane. The rotation axis, that is, the first rotation axis, of the first rotational motion has to be parallel to the vertical direction (the z axis direction in FIGS. 7A and 7B). The first rotational motion does not need to describe, for example, a circle, but has only to describe an arc sufficient to specify the first rotation axis.

Therefore, a motion in which a user swings up and down a golf club as illustrated in FIG. 7A may be used as the first rotational motion. In FIG. 7A, the rotation axis r (corresponding to the first rotation axis herein) is almost parallel to the ground surface and is not parallel to the z axis. The first rotational motion illustrated in FIG. 7A may be executed, for example, as a warming-up motion before starting a golf swing. This warming-up motion is not troublesome to a user nor gives a large burden to the user.

In this embodiment, the golf swing itself of the user may be used as the first rotational motion as illustrated in FIG. 7B. In FIG. 7B, the rotation axis r is directed to the oblique front-upper side of the user and is not parallel to the z axis. At this time, since a motion other than the golf swing is not required, the user does not have to recognize the first rotational motion. The golf swing as the first rotational motion may be a swing of actually hitting a ball or a practice swing. Particularly, only a down swing before impact (before the lowest point in case of the practice swing) which draws a clear circle may be extracted and used as the first rotational motion.

The CPU 200 (see FIG. 5) serves as the data acquiring unit 202, the calculation unit 204, and the azimuth correcting unit 206 in accordance with a program and performs the following processes. The CPU 200 receives measurement data based on the first rotational motion. Here, the CPU 200 acquires the angular velocities omega [rad/s] measured with the inertial sensor 111 (see FIG. 4) on the basis of the first rotational motion for each measurement unit 10 and for each axis component in the form of Expression (1).

[Math. 1]

ω=(ω_(x), ω_(y), ω_(z))   (1)

On the other hand, the quaternion q calculated by the CPU 200 in order to tune the axes of the measurement units is expressed by Expression (2). The rotation angle is defined as theta and the unit vector of the rotation axis is defined as (r_(x), r_(y), r_(z)).

$\begin{matrix} \left\lbrack {{Math}{.2}} \right\rbrack & \; \\ {q = {\left( {w,x,y,z} \right) = \left( {{\cos \frac{\theta}{2}},{r_{x}\sin \frac{\theta}{2}},{\sin \frac{\theta}{2}},{r_{z}\sin \frac{\theta}{2}}} \right)}} & (2) \end{matrix}$

Here, the magnitude |omega| of an angular velocity omega of one sample given as the measurement data is expressed by Expression (3) and means a rotation angle per unit time.

[Math. 3]

|ω|=√e,rad ω_(x) ²+ω_(y) ²+ω_(z) ²   (3)

Accordingly, the quaternion deltaq representing a rotation per unit time can be expressed by Expression (4) using |omega|.

$\begin{matrix} \left\lbrack {{Math}{.4}} \right\rbrack & \; \\ {{\Delta \; q} = \left( {{\cos \frac{\omega }{2}},{\frac{\omega_{x}}{\omega }\sin \frac{\omega }{2}},{\frac{\omega_{y}}{\omega }\sin \frac{\omega }{2}},{\frac{\omega_{z}}{\omega }\sin \frac{\omega }{2}}} \right)} & (4) \end{matrix}$

That is, the quaternion deltaq representing a rotation per unit time can be created from the measurement data. Here, a posture variation during a given time is given as an integral of the rotation per unit time. When the number of samples at time t is assumed to be N, the quaternion q(t) at arbitrary time t is obtained as expressed by Expression (5).

[Math. 5]

q(t)=Δq(0)Δq(1) . . . Δq(N)   (5)

That is, the quaternion q(t) is calculated by integrating deltaq of all the samples. In the calculation of Expression (5), it is assumed that a process of normalizing the resultant value for each integration is performed. The normalization process is expressed by Expression (6).

$\begin{matrix} \left\lbrack {{Math}{.6}} \right\rbrack & \; \\ {{q(i)}_{nor} = \frac{q(i)}{{q(i)}}} & (6) \end{matrix}$

As described above, the quaternion q(t) at arbitrary time t can be calculated.

Here, it is assumed that the quaternion q(t1) of a first posture and the quaternion q(t2) of a second posture are calculated by Expression (5). For example, when a motion in which a user swings up and down a golf club as illustrated in FIG. 7A is used as the first rotational motion, the first posture may correspond to the lowest head position of the golf club and the second posture may correspond to the highest head position. At this time, the quaternion q_(r) representing the rotation varying from the first posture to the second posture can be calculated by Expression (7).

[Math. 7]

q _(r)=(q _(rw) , q _(rx) , q _(ry) , q _(rz))=q(t2)q(t1)⁻¹   (7)

Here, q(t1)⁻¹ represents the inverse quaternion of q(t1). The rotation angle theta_(r) and the rotation axis vector (x_(r), y_(r), z_(r)) in the rotation varying from the first posture to the second posture can be calculated by Expressions (8) to (11). As expressed by Expression (7), elements of the quaternion q_(r) are q_(rw), q_(rx), q_(ry), q_(rz). The rotation axis vector corresponds to the information of the rotation axis according to the invention.

$\begin{matrix} \left\lbrack {{Math}{.8}} \right\rbrack & \; \\ {\theta_{r} = {2a\; {\cos \left( q_{rw} \right)}}} & (8) \\ {x_{r} = \frac{q_{rx}}{\sin \left( \frac{\theta_{r}}{2} \right)}} & (9) \\ {y_{r} = \frac{q_{ry}}{\sin \left( \frac{\theta_{r}}{2} \right)}} & (10) \\ {z_{r} = \frac{q_{rz}}{\sin \left( \frac{\theta_{r}}{2} \right)}} & (11) \end{matrix}$

The rotation angle theta_(r) is obtained by calculating the arc cosine of q_(rw) as expressed by Expression (8). As expressed by Expressions (9) to (11), the rotation axis vector (x_(r), y_(r), z_(r)) is obtained from the rotation angle theta_(r) and q_(rx), q_(ry), q_(rz). Since the information of the rotation axis is obtained from the quaternion q_(r) of Expression (7), the quaternion q_(r) corresponds to the first transform expression according to the invention.

In this embodiment, the vertical direction can be detected on the basis of the gravitational acceleration and one axis direction (herein, the z axis direction) of the measurement units can be tuned. Accordingly, when the azimuth angles on the horizontal plane in the measurement units can be calculated, it is possible to three-dimensionally tune the azimuths. Therefore, the CPU 200 can determine the azimuth angles of the measurement units by the use of the vector (x_(r), y_(r)) on the horizontal plane in which the z axis direction of the rotation axis vector (x_(r), y_(r), z_(r)) is ignored. At this time, the vector (x_(r), y_(r)) on the horizontal plane in one measurement unit may be used as a reference direction to determine the azimuth angles of the measurement units or a specific direction (for example, the x axis) of an absolute coordinate system may be used as a reference direction.

In this way, the CPU 200 can determine the azimuth angles of the measurement units by serving as the data acquiring unit 202, the calculation unit 204, and the azimuth correcting unit 206 in accordance with a program to perform the processes using the above-mentioned expressions and can tune the azimuths on the horizontal plane on the basis of the azimuth angles.

In the elevation angle direction about the horizontal plane, the azimuths of the measurement units can be tuned using the existing technique based on the gravitational acceleration. Although detailed description will not be described, it is possible to tune the azimuth in the elevation angle direction, for example, from the angle formed by a vector based on the gravitational acceleration and the z axis.

Accordingly, since the CPU 200 can tune three axis directions of the plural measurement units, it is possible to accurately analyze a user's golf swing.

Flowchart

FIGS. 8 and 9 are flowcharts illustrating an example of a motion analysis method in the motion analysis system 1. FIG. 8 is a flowchart illustrating a process flow in the measurement unit 10 and FIG. 9 is a flowchart illustrating a process flow in the analysis control device 20. The control unit 116 of the measurement unit 10 and the CPU 200 of the analysis control device 20 may perform the process flows in accordance with a program.

As illustrated in FIG. 8, the control unit 116 of the measurement unit 10 waits until a measurement start command is given, that is, until a measurement start command is received from the analysis control device 20 (N in S10). Then, when the measurement start command is received (Y in S10), the acceleration based on the stop state of a user is measured and the created measurement data is stored in the storage unit 115 (S20).

The acceleration of the measurement data at this point includes only information of the gravitational acceleration and the CPU 200 of the analysis control device 20 can tune the azimuth of the plural measurement units in the elevation angle direction about the horizontal plane. Step S20 and step S30 to be described later may be reversed in the processing order.

The control unit 116 of the measurement unit 10 measures the angular velocity based on the first rotational motion of the user and the created measurement data is stored in the storage unit 115 (S30). The CPU 200 of the analysis control device 20 can tune the azimuth on the horizontal plane of the plural measurement units using the above-mentioned expressions on the basis of the measurement data. The CPU 200 can tune the three axis directions of the plural measurement units on the basis of the measurement data of steps S20 and S30.

The control unit 116 of the measurement unit 10 causes the inertial sensor 111 to measure the acceleration and the angular velocity based on the user's swing and stores the created measurement data in the storage unit 115 (S50). At this time, the measurement data includes the accelerations in the x axis direction, the y axis direction, and the z axis direction measured by the acceleration sensor and the angular velocities around the x axis, the y axis, and the z axis measured by the angular velocity sensor.

Thereafter, when a measurement stop command is given, that is, when the measurement stop command is received from the analysis control device 20 (Y in S70), the measurement data stored in the storage unit 115 is transmitted to the analysis control device 20 (S80). The process flow goes back to step S10 and waits until a next measurement start command is received from the analysis control device 20.

When the measurement stop command is not given (N in S70), the process flow goes back to step S50 and the control unit 116 causes the inertial sensor 111 to measure the acceleration and the angular velocity based on the user's swing and to create measurement data.

On the other hand, as illustrated in FIG. 9, the CPU 200 of the analysis control device 20 serves as the main control unit 203 and instructs the measurement unit 10 to start measurement (S210). That is, the CPU 200 transmits the measurement start command to the measurement unit 10.

Then, the CPU 200 waits until the measurement unit 10 acquires satisfactory measurement data (N in S240). When the measurement unit 10 acquires satisfactory measurement data (Y in S240), the CPU 200 instructs the measurement unit 10 to stop the measurement (S250). That is, the CPU 200 transmits the measurement stop command to the measurement unit 10.

The CPU 200 of the analysis control device 20 serves as the data acquiring unit 202 and receives the measurement data from the measurement unit 10 (S260). First, the CPU 200 acquires information on the vertical direction for each measurement unit from the acceleration based on the stop state of the user. Specifically, the angle thetaz formed by the direction of the gravitational acceleration and the z axis is obtained (S270). Accordingly, it can be seen how the z axis of each measurement unit is inclined in comparison with the direction of the gravitational acceleration (that is, the vertical direction).

Then, the CPU 200 calculates the first transform expression including information of the first rotation axis for each measurement unit from the angular velocity based on the first rotational motion of the user out of the measurement data (S300). Here, the first transform expression is specifically the quaternion q_(r) of Expression (7) and the rotation axis vector (x_(r), y_(r), z_(r)) calculated by Expressions (8) to (11) is the information of the first rotation axis. Step S300 may be performed before step S270.

Then, the CPU 200 of the analysis control device 20 analyzes the user's golf swing on the basis of the measurement data. At this time, the CPU 200 tunes the azimuth in the elevation angle direction about the first plane (herein, the horizontal plane) in the plural measurement units on the basis of the angle thetaz calculated in step S270 (S400). The CPU 200 tunes the azimuth on the first plane (herein, the horizontal plane) in the plural measurement units using the first transform expression (S410).

Specifically, the CPU 200 acquires a vector (x_(r), y_(r)) on the horizontal plane in which the z axis direction is ignored from the rotation axis vector (x_(r), y_(r), z_(r)) obtained by the first transform expression. For each measurement unit, the vector (x_(r), y_(r)) on the horizontal plane and the reference direction are compared to obtain an azimuth angle. Accordingly, it is possible to tune the azimuth on the horizontal plane in the plural measurement units on the basis of the azimuth angles. Step S400 may be performed before step S410.

Then, the CPU 200 analyzes the swing from the measurement data based on the user's golf swing (S460). Since the azimuths in the plural measurement units are three-dimensionally tuned in steps S400 and S410, it is possible to accurately analyze a swing.

As described above, the motion analysis system 1 and the motion analysis method according to this embodiment can tune the axis directions of the plural measurement units 10 used to detect a motion after attachment thereof and can perform accurate motion analysis. At this time, the user has only to do the stopping and the first rotational motion and thus complicated motions or a motion giving a large burden is not required.

2. Second Embodiment

In the first embodiment, each measurement unit 10 includes the acceleration sensor. Accordingly, the z axis directions of the plural measurement units 10 can be tuned on the basis of the gravitational acceleration. However, when each measurement unit 10 does not include the acceleration sensor or when a user cannot stop, it is not possible to tune the z axis directions. For example, when a motion of a user on a moving object (for example, a vehicle) is analyzed, it may be difficult for the user to stop. A motion analysis system 1 according to a second embodiment can tune three axis directions of plural measurement units without using the acceleration sensor.

Configuration of Motion Analysis System

As described above, the azimuths on the first plane in the plural measurement units can be tuned in the first embodiment. Here, when the azimuth on a second plane (that is, the elevation angle in the first plane) perpendicularly intersecting the first plane can be tuned, it is possible to three-dimensionally tune the azimuths even when the coordinate axes are not tuned at all. That is, by repeating the same technique as in the first embodiment two times and calculating two quaternions having different rotation axes, it is possible to three-dimensionally tune the azimuths.

At this time, when each measurement unit 10 does not include the acceleration sensor or when a user cannot stop, it is possible to tune the axes of the plural measurement units by causing the user to do a second rotational motion having a different rotation axis in addition to the first rotational motion.

The configuration of the motion analysis system 1 according to the second embodiment is the same as in the first embodiment (see FIG. 1) and description thereof will not be repeated. However, unlike the first embodiment, the measurement data (measurement data based on the first rotational motion and the second rotational motion) used to tune the axes has only to include the information of the angular velocity from the inertial sensors 111-1 and 111-2 (see FIG. 1). The measuring of a golf swing (see FIGS. 2 and 3) in the motion analysis system 1 or the blocks (see FIGS. 4 and 5) of the measurement unit 10 and the analysis control device 20 are the same as in the first embodiment and description thereof will not be repeated.

In the motion analysis system 1 according to the second embodiment, it is necessary to do two rotational motions unlike the first embodiment. These rotational motions are a first rotational motion (the same as in the first embodiment) around a first rotation axis and a second rotational motion around a second rotation axis respectively. Here, the first rotation axis and the second rotation axis need to be different from each other. For example, the motion illustrated in FIG. 7A may be used as the first rotational motion and the motion illustrated in FIG. 7B may be used as the second rotational motion.

In the motion analysis system 1 according to the second embodiment, the processes which are performed using Expressions (1) to (11) by the CPU 200 of the analysis control device 20 in the first embodiment are carried out on the measurement data based on the second rotational motion in addition to the measurement data based on the first rotational motion. Hereinafter, processes in the second embodiment different from those in the first embodiment will be described with reference to flowcharts.

FIGS. 10 and 11 are flowcharts illustrating an example of a motion analysis method in the motion analysis system 1 according to this embodiment. FIG. 10 is a flowchart illustrating a process flow in the measurement unit 10 and FIG. 11 is a flowchart illustrating a process flow in the analysis control device 20. The control unit 116 of the measurement unit 10 and the CPU 200 of the analysis control device 20 may perform the process flows in accordance with programs. The same steps as in FIGS. 8 and 9 will be referenced by the same reference numerals, description thereof will not be repeated, and only the steps different from those in the first embodiment will be described below.

As illustrated in FIG. 10, the control unit 116 of the measurement unit 10 does not perform step S20 (see FIG. 8) of acquiring the measurement data based on the gravitational acceleration unlike the first embodiment. The control unit 116 of the measurement unit 10 measures the angular velocity based on the second rotational motion of the user after step S30 and stores the created measurement data in the storage unit 115 (S40).

On the other hand, as illustrated in FIG. 11, the CPU 200 of the analysis control device 20 does not perform steps S270 and S400 (see FIG. 9) using the measurement data based on the gravitational acceleration unlike the first embodiment. The CPU 200 of the analysis control device 20 performs step S320 using the measurement data based on the second rotational motion after step S300. That is, a second transform expression including information of the second rotation axis is detected from the angular velocity based on the second rotational motion of the user out of the measurement data for each measurement unit (S320).

Here, the second plane is a plane perpendicular to the first plane. For example, when it is assumed that the first plane is a plane formed by the x axis and the y axis of a certain coordinate system, the second plane is, for example, a plane formed by the y axis and the z axis. Here, the first rotation axis does not need to be parallel to the z axis and the second rotation axis does not need to be parallel to the x axis. The determination of the azimuth angle on the second plane corresponds to the determination of the elevation angle about the first plane. The determination of the azimuth angle on the second plane corresponds to the calculation of the angle thetaz formed by the direction of the gravitational acceleration and the z axis in the first embodiment. The first plane in the first embodiment is the horizontal plane, but the first plane in this embodiment is not limited to the horizontal plane and, for example, a plane inclined from the horizontal plane may be used.

The CPU 200 of the analysis control device 20 analyzes the user's golf swing on the basis of the measurement data, and tunes the azimuths on the second plane in the plural measurement units using the second transform expression (S420).

The azimuths on the second plane perpendicular to the first plane as well as the azimuths on the first plane can be tuned in plural measurement units through steps S320 and S420. Therefore, it is possible to three-dimensionally tune the axes in the plural measurement units.

The calculations of the CPU 200 in steps S320 and S420 are the same as the processes (step S300 and S410) based on the first rotational motion and detailed description thereof will not be repeated. The order of steps S300 and S320 and the order of steps S410 and S420 may be reversed.

As described above, the motion analysis system 1 and the motion analysis method according to this embodiment can tune the axis directions of the plural measurement units 10 used to detect a motion after attachment thereof and can perform accurate motion analysis. At this time, the user has only to do the first rotational motion and the second rotational motion and thus complicated motions or a motion giving a large burden is not required. Unlike the first embodiment, since the information of the gravitational acceleration may not be used to tune the axes, the user does not need to be in a stop state.

The invention is not limited to these embodiments and includes a configuration (for example, a configuration having the same functions, methods, and results or a configuration having the same objects and advantages) which is substantially the same as the configuration described in the embodiments. The invention also includes a configuration in which non-essential elements of the configuration described in the embodiments are replaced. The invention also includes a configuration exhibiting the same operational advantages or achieving the same objects as the configuration described in the embodiments. The invention also includes a configuration in which known techniques are added to the configuration described in the embodiments.

REFERENCE SIGNS LIST

1: Motion analysis system

10: Measurement unit

10-1: Measurement unit

10-2: Measurement unit

20: Analysis control device (PC)

30: Golf club

111: Inertial sensor

111-1: Inertial sensor

111-2: Inertial sensor

112 x: Acceleration sensor

112 y: Acceleration sensor

112 z: Acceleration sensor

113 x: Angular velocity sensor

113 y: Angular velocity sensor

113 z: Angular velocity sensor

115: Storage unit

116: Control unit

118: Communication unit

200: CPU

201: Motion analysis unit

202: Data acquiring unit

203: Main control unit

204: Calculation unit

206: Azimuth correcting unit

210: Communication unit

220: Operation unit

230: ROM

240: RAM

250: Recording medium

260: Display unit

A: Swing path

P1: Swing start position

P2: Top position

P3: Impact position

P4: Follow-through top position

r: Rotation axis 

1. A motion analysis system comprising an analysis control device that analyzes a motion of a measurement target using measurement data from a plurality of measurement units including an angular velocity sensor, wherein the analysis control device receives measurement data based on a first rotational motion around a first rotation axis of the measurement target from the plurality of measurement units, and tunes azimuths on a first plane in the plurality of measurement units using the measurement data based on the first rotational motion.
 2. The motion analysis system according to claim 1, wherein the first rotation axis is an axis intersecting a perpendicular line with respect to the first plane.
 3. The motion analysis system according to claim 1, wherein a first transform expression including information of the first rotation axis is acquired for each measurement unit, and wherein the azimuths on the first plane in the plurality of measurement units are tuned using the first transform expressions.
 4. The motion analysis system according to claim 1, wherein the first plane is a horizontal plane.
 5. The motion analysis system according to claim 4, wherein each of the plurality of measurement units includes an acceleration sensor, and wherein the analysis control device tunes the azimuths in an elevation angle direction about the first plane in the plurality of measurement units using information of a gravitational acceleration included in the measurement data of the acceleration sensors when the measurement target stops.
 6. The motion analysis system according to claim 1, wherein the analysis control device receives measurement data based on a second rotational motion around a second rotation axis of the measurement target from the plurality of measurement units when an axis intersecting a perpendicular line with respect to a second plane perpendicular to the first plane is set as the second rotation axis, and tunes azimuths on the second plane in the plurality of measurement units using the measurement data based on the second rotational motion.
 7. The motion analysis system according to claim 1, wherein the measurement units are attached to at least one of exercise equipment and a test subject.
 8. The motion analysis system according to claim 1, wherein the analysis control device uses at least a part of a swing motion as the first rotational motion.
 9. The motion analysis system according to claim 1, wherein the motion analysis system includes the plurality of measurement units.
 10. An azimuth tuning method comprising: receiving measurement data based on a first rotational motion around a first rotation axis of a measurement target from a plurality of measurement units including an angular velocity sensor; and tuning azimuths on a first plane in the plurality of measurement units using the measurement data based on the first rotational motion. 